The installation failed because both emacs-snapshot-common and emacs25-common contain /usr/share/emacs/site-lisp/subdirs.el.

There are a number of ways to get past this, but it’s worth considering that the Emacs packages, in spite of the fact that they include a version number in their name, are not designed to be co-installable. (In fact, starting with Debian 10 and Ubuntu 18.10, the packages no longer include the version number in their name.)

The cleanest way to fix this it to divert one of the package’s copy of the file; for example, to keep emacs25’s copy: